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The OB7 -2WARC is a high performing WARC Duoband Antenna for the 18 and 24 MHz amateurradio bands.

OptiBeam shortwave antennas are designed and optimized by support of modern techniques such ascomputerized antenna simulation and are finally adjusted by extensive tests in praxis.

The core of the antenna consists of a direct coupled 2-element-drivercell where the drivers areconnected with a phase line of square tubes.

There is a separate reflector for each of the two bands. Furthermore there is a separate director forthe 17m band and two separate directors for the 12m band.

By this new concept of feeding in combination with a special order of all elements and the exclusiveuse of full size elements highest efficiency, optimum bandwidth concerning high gain, clear patternand low SWR together with unlimited power handling are achieved.

17m 112m5,1/6,0

10,6/11,524/22

1,11,0507

3/48,505,1018

average gain over a dipole in free spacegain of monobanders for comparison: 2-element Vagi: 4 dbd, 3-element Vagi: 5-6 dbdaverage gain at 20m above ground

The included schematic diagram is needed for the assembly and the following information is given:

-> type of element (R=Reflector, S=Driver, D = Director) and the position on the boom-> measurements of the element sections (length and diameter)-> lengths of the element halves-> distances between the elements.

2.1 Sorting the parts

The antenna partly consists of already pre assembled parts.All parts of the antenna are marked.For faster and easier assembly it is recommended to sort the parts per band.

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2.2 Assembly of boom

The square boom consists of three parts which have to be assembled each by two couplingpieces that are already installed at one side of the boom parts.For each coupling piece 4 screws are needed. The screws have to be tightened finally not beforethe parts of the boom really fit to each other perfectly.

2.3 Construction of the elements

For the element to boom brackets 4-cornered plates are used and the insulation of the elementsis done by 2 special plastic tube holders (see picture page).

The middle sections of the elements have to be fixed exactly centred on the plates (orientation= black middle line on parasites I insulator middle piece on driven elements). For that theelement middle sections have to be put in to the tube holders (only concerning the drivenelements one tube holder has to be opened for this process). Then the screws of the tubeholders have to be tightened solidly. The screws of the driver middle sections divided with theinsulators have to point straight upwards.

~ Next the other element sections have to be assembled. Insert the following sections in theprevious sections with their side which has two drill-holes equal in size. The tubes have to beput in until the drill-holes of both sections overlap perfectly (concerning the outer 12mm tubes ofthe driven elements the middle one of the three drill-holes has to be chosen).Then the corresponding screws (20mm tube = longer screw I 16mm tube = shorter screw) haveto be pushed through from the side of the enlarged drill-hole of the previous segment. On theopposite side the washers have to be inserted and the self securing nuts have to be screwed onand tightened solidly (hold the screw heads with the included special screw-driver againstturning, the screw heads dive into the enlarged drill-hole, see picture page). This method resultsin an extremely solid mechanical connection and rattle sounds inside the segment overlaps aretotally avoided.

By this way of assembling the element sections the required lengths of the sections and theelement halves are achieved automatically.

While mounting the elements pay attention that all screw heads show upwards. Keep in mindthat the elements hang below the boom. Therefore the screw heads have to be on the same sideof the elements where the plates are located at.

2.4 Attaching the elements to the boom

The elements fixed on the plates have to be mounted on the underside of the boom at themarked positions while the connecting screws of the boom should remain horizontal. The squareboom makes a straightening of the elements unnecessary.The plates are attached to the boom by 2 square brackets which embrace the boom from the topand 4 self securing nuts (see picture page). When tightening the square brackets pay attentionthat all elements are parallel to each other.

The driven elements (from the rear 812, 817) should not be tightened before the installation ofthe phase line is done (see fig. 2.5) as they might have to be moved slightly on the boom.

The plates of the outer elements end directly in line with the tips of the boom.

In case the antenna cannot be reached easily while assembling or even for more convenience ingeneral we recommend to assemble the driver cell together with the phase line and the coaxconnector separately and then mount it below the boom in one piece.

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2.5 Installation of the phase line

The driven elements (512,517) are connected with 2 parallel20mm square tubes (=phase line).

The square tubes have to be in direct contact to the elements (put the washers only below thescrew heads). First remove the element screws and washers. Then insert the predrilled squaretubes (move the elements slightly if needed) by means of the element screws. Likewise insert thecoax connector at the bottom of the phase line (=elements below boom) directly with the screwsof 512 (see picture page). Be sure that the screw at the backsite of the connector which holdsthe strap is tightened solidely.Finally the phase line square tubes have to be tightened really solidly together with the drivenelements (=important electrical contact) and the driven elements have to be mounted below theboom by means of the element plates (see fig. 2.4).

2.6 Installation of the boom to mast clamp

The boom-to-mast clamp is a completely pre assembled part (see picture page).It has to be attached slightly out of the balance point between 512 and 517.

The feeding of the antenna is done by 50 Ohm coax cable.For connection a PL-259 connector is required. The connector should be sealed against water entry.

Close to the feed point the cable should be winded to a choke coil with 5 to 6 turns of about 20 cm ofdiameter. Hereby the antenna is electrically balanced and unwanted radiation of the cable itself isprevented.Instead of the choke coil a 1:1 balun can be used as well.

By some influences of the direct surroundings it may happen that the resonance of the antenna(=point of best 5WR) shifts on one or several bands.By minimum changes of the according driver lengths (=shortening or lengthening of the outer 12mmsections) the resonant frequency of the according band can be shifted to the desired point.By a slight decrease of the lengths of both element halves (put outer section in to the last drill-hole)the resonant frequency will be shifted upwards, by an increase (pull final section out to the first drill-hole) it will be shifted downwards.

Normally these adjustments don't have to be done as the antenna does not react very sensitiveagainst influences of the surroundings and the 5WR curve is flat anyway.

At strong winds the antenna should be placed in a way that the tips of the elements show straightinto the wind which means that the boom stands broadside to it.Hereby physical stress to the full size elements is avoided and their duration is enlarged.

OptiBeam OB7-2WARC

1,15

d201,15

. d20

1,05

d 16 D12b (2,78)D17 (3,75)1,15

d 12

3,201,15 1,05 D12a (2,83)d20 d 16

2,501,15 1,45 1,50 817 (4,10)d20 d 16 d 12

1,751,15 1,05 812 (3,03)d20 d 16

1,15

d201,15

d20

1,05

d 16R12 (3,10)

R17 (4,25)1,45

d 16

1,65

d 12

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Ansicht Element-PlattfonnStrahlerelement mitPhasenleitung(+ PhasenleitungsstubModell OB9.S) Iview element platfonndriven element withphaseline (+ phase line stubmodelOB9-S)

Ansicht Koax-AnschluBbuchse S0239 mit Strahler-element und Phasenleitung /view coax connector S0239 with driven elementand phaseline

Ansicht Elemenmbergange 2S/2Omm- 20/16mm . 16/12mm Iclose up view element transitions 2S/20mm - 20116mm- 16112mm

Thomals Schmenger, DF2BORastatter StraBe 370-75179 Pforzheim,Tel.: I Fax +49-7231-453153